Confounded by Standpipe calculations

[RainbowFS]

Trying to be brief, I'm involved in a hospital remodel that has two dry 6" standpipes (circa 1972) about 200 ft. apart. The remodel means that the FDC of one of them is going away. It was decided to interconnect the standpipes across the 4th floor roof to fix the problem.
The original hospital retained engineer declined to handle the project at the last minute and this got dropped in my lap.
I thought that running a six inch line across the roof would be the logical approach, but the fire marshal wants calcs.
I have a sprinkler calc program, two actually. (Sigma7700, 8800) So I've been trying to fill the slots in that program to get a workable equation, but it just isn't coming out.
So- the info I do have is:
The standpipe rises 55 ft. from FDC(5" Storz) to the high point, then about 220 ft. over to the top of the other one.
The AHJ gave me some fire truck info, their smallest pump truck: this is what I got
1000 gpm @ 150 psi.
700 " @ 200 "
500 " @ 250
City water flow from a near by hydrant is
Stat- 68.5
Res - 61, flowing 10,000 gpm

I'm told I need to flow 750 gpm (three points, highest, most remote, and one in the primary riser, I think)

Filling the formulae is the where the problem is, I hope.
Is the K-factor of a 2 1/2" valve flowing 250 gpm @ 100 psi, 10?

I am familiar with my sprinkler calc program, but applying it to this situation has my stumped.

My eternal thanks to any insight here.

 

[TravisMack]

Start with the basic formula: Q=k(p)^.5
Then, k=Q/p^.5. This gives you a k value of 25.

That should get your started. Don't forget to include friction losses for your hose valve, nipple and tee. Many times, people don't include those losses which can be 5-7 psi and it causes the system to not work at test time.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[MGXFP]

I use HydraCALC so this may not apply.

Put a hose flow (like your hose flows for the outside hydrants for sprinkler systems) on the hose valve, include a short length of pipe and the friction loss for the valve and tee.

If you have two standpipes you want the most remote flowing the top two valves at 250 GPM each and the second standpipe's top valve flowing 250 GPM.

Hope this helps, TravisMack lined me out on this subject a while back.

 

[TravisMack]

If I recall correctly, Sigma doesn't allow the hose flows like HydraCalc, HASS and many others do. It has been many years since I used Sigma. With Sigma, I believe you have to put in a k factor and pressure that equates to the flow you want. By using a K of 25 and pressure of 100, you get a flow of 250 using the standard formula Q=k(p)^.5

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[spkreng]

hey guys the remote standpipe has to have a flow of 500 gpm and then add 250 for each thereafter, so node A 250 gpm, k=25 TO node B - 250 gpm (2 hose valves 1'-0" apart) then junction of second standpipe add 250 gpm (deduct) ama right here?

 

[SprinklerDesigner2]

spkreng,

The answer to your question is no.

Friction loss through 2 1/2" sch. 40 at 500 gpm is .777 psi/linear foot.

The top outlet of the most remote standpipe has to flow 250 gpm so k=250/100^.5 or k=25 if you want to use the computer.

If dong it by hand the k-factor is irrelevant. The only reason we need a k-factor is we want to make the computer work.

On something this simple I find it easier to just do it all by hand. It's only 6 or 7 steps.

Yes, it is 500 gpm at the remote standpipe but not the top outlet of the most remote standpipe. You flow 250 gpm from the top outlet then add another 250 gpm at the next outlet directly below for a total of 500 gpm.

Give me a few minutes and I'll make up a quick hand calc and post it so you can see what I am doing.

 

[SprinklerDesigner2]

spkreng,

For fittings that aren't in 13 I refer to the Crane Company piping manual. In their table of fittings and valves, an 2 1/2 inch angle valve is equivalent to 33 feet of 2 1/2 inch steel pipe. So at a flow of 250 gpm, you lose about 7.1 psi. When you add the tee and 1’-0” C-C nipple the total equivalent length will be 33+12+1=46 feet which will produce 9.9 psi head loss.

 

[SprinklerDesigner2]

spkreng,

I misread your post. You are correct.

 

[spkreng]

hey i just call em as i see em, been designing for 28 years lots of times i'm wrong (tunnel vision) which is why i joined this...also guy's there is an informative forum like this at sprinklerforum@firesprinkler.org you might like

 

[SprinklerDesigner2]

I prefer to calculate standpipe systems by hand. They are easy enough to do in just a couple minutes and you don't have to spend the time tweaking k-factors to force HASS to come up with the right answer.

My example is only 5 steps and the most I've ever had is maybe 7 or 8. Five minutes tops and you are done.

As far as elevation it doesn't matter if it is added in pieces or all at one time. In this example I added elevation individually between reference points but I could have just as easily added it all one time.

A decent reference for friction loss through fire hose is available at

http://www.elkhartbrass.com/files/aa/downloads/performance/ Fire Hose Friction Loss.pdf

Stick drawing of the standpipe system I calculated.

http://img263.imageshack.us/img263/448/standpipeexample1.jpg

My calculations.

http://img176.imageshack.us/img176/1798/standpipeworksheet.jpg

 

[SprinklerDesigner2]

"hey i just call em as i see em, been designing for 28 years lots of times i'm wrong (tunnel vision)..."

I've been doing it for 35 years and hope to be doing it another 25 because I love it. In 35 years I've never dreaded a Monday morning which makes me the luckiest man in America.

But the tunnel vision is so right on target.

 

[chicopee]

Instead of calculations using formulae, use the hydraulic graph sheet (N^1.85) to get an idea how much water will be available at the proposed connection.You can see an example of such graph sheet in my answer to civilchica's questionon 4/12/'10.
Procedure that I would use is as follows:
1. Plot the hydrant flow test results-straight line.
2. Deduct from curve 1., the friction loss between hydrant and the base of the standpipe. That new curve will represent(approximately) the water supply curve at the base of the riser.
3. Deduct the static pressure from the 55' elevation from new curve 2.
4. Deduct the friction loss from the base of the standpipe to the new cross connection to get a new water supply curve.

Note there could be additional deductions in the above procedure for fire hose streams needed for that building; there could be further deduction or increase in static pressures between the fire hydrant and the base of the riser.

Also the friction loss deductions may not be straight forward because of changes in pipe sizes, so if you have more than one pipe size you will need to do friction loss deduction for these different pipes on that graph.

 

[RainbowFS]

Thank you SD2! Your example worked perfectly for my situation. I was able to reduce the over-the-roof pipe size to 4" and still fit within the capability of the fire pump provided by the city.
I appreciate your help.

 

[cocchiarale]

On Sigma 7700 for standpipe calculation you must enter on the S line a K factor of 65, number of sprinkler enter 1 and the minimum flow of 500 gpm for your most remote Standpipe and on the F line enter your node point at your feed connection to the other standpipe and add 250 gpm flow, insert all your nodes from your supply up to your flow point. I hope this will help you.